The Anterior Triangle

is bounded anteriorly by the midline of the neck and posteriorly by the sternocleidomastoid muscle. Its superior boundary is formed by the lower border of the mandible and a line drawn from the angle of the mandible to the tip of the mastoid process. This triangle may be subdivided as follows:

• 1
  

  Submandibular triangle

  
  
• 2
  

  Submental triangle

  
  
• 3
  

  Carotid triangle

  
  
• 4
  

  Muscular triangle

The Posterior Triangle

is limited anteriorly by the sternocleidomastoid, posteriorly by the trapezius, and below by the middle third of the clavicle. This is further divided by the posterior belly of the omohyoid into the following:

• 5
  

  Occipital triangle

  
  
• 6
  

  Subclavian triangle

1

Thyroid Cartilage

is especially prominent where the right and left laminae of this cartilage fuse in the upper midline of the neck, which is referred to as the laryngeal prominence or Adam’s apple.

2

Hyoid Bone

is located in the midline about 1 inch above the laryngeal prominence and in line with the lower border of the third cervical vertebra. If followed laterally, the greater cornu may be palpated. Its tip lies about midway between the laryngeal prominence and the mastoid process and is an important surgical landmark for the ligation of the lingual artery.

3

Cricoid Cartilage

lies just below the thyroid cartilage and at the level of the sixth cervical vertebra.

1

External Jugular Vein

descends superficial to the sternocleidomastoid muscle and pierces the deep cervical fascia in the posterior triangle to empty into the subclavian vein. The deep fascia is firmly attached to the vein wall as this vein pierces the fascia. This prevents collapse of the vein if it is accidentally cut.

2

Anterior Jugular Vein

begins in the suprahyoid region and descends near the midline parallel with its partner of the opposite side. Just above the clavicle, it pierces the deep fascia, passes beneath the sternocleidomastoid, and empties into the external jugular. It is often connected with the vein of the opposite side above the sternal notch, forming the jugular venous arch.

3

Vein of Kocher

often arises from the branches of the common facial vein, descends along the anterior border of the sternocleidomastoid, and drains into the jugular venous arch or the internal jugular. If the anterior jugular is absent, this vein usually is large.

4

Superficial Cervical Plexus

arises from the anterior primary divisions of cervical segments C2 to C4.

• A
  

  Lesser occipital (C2)–hooks around the spinal accessory; ascends along the posterior border of the sternocleidomastoid muscle; and terminates in auricular, mastoid, and occipital branches.

  
  
• B
  

  Great auricular (C2 to C3)–takes exit from under the middle of the posterior border of the sternocleidomastoid and extends upward posterior to and parallel with the external jugular vein.

  
  
• C
  

  Transverse cervical (C2 to C3)–exits just below the great auricular and extends across the sternocleidomastoid to the anterior triangle, where it fans out to supply the skin between mentum and sternum.

  
  
• D
  

  Supraclavicular (C3 to C4)–exits from the middle of the posterior border of the sternocleidomastoid and divides into three terminal branches:

  
  
  
  
  • 1
    

    Anterior–extends downward, innervating the skin as far as the second intercostal space and the sternoclavicular joint.

    
    
  • 2
    

    Middle–descends over the middle third of the clavicle, at times piercing this bone, thereby causing persistent neuralgia if involved in the callus following fractures of the clavicle.

    
    
  • 3
    

    Posterior–is distributed to the skin over the upper two thirds of the deltoid and the acromioclavicular joint.

  
  

1

Common Carotid

the right common carotid arises as a terminal branch of the innominate artery, whereas the left common carotid arises directly from the arch of the aorta. In the carotid triangle, it is superficial in position and therefore readily palpable at the anterior border of the sternocleidomastoid, which partly overlaps it in the lower portion of the triangle. Only a few tributaries of the internal jugular vein, branches of the cervical plexus, and the omohyoid cross superficial to the artery. Digital compression to halt the flow of blood is placed at the anterior border of the sternocleidomastoid at the level of the cricoid, with pressure exerted posteriorly against the carotid tubercle on the transverse process of the sixth cervical vertebra (tubercle of Chassaignac). The artery gives off no branches in the neck and ascends to a point -inch below and behind the greater cornu of the hyoid, or approximately at the upper border of the thyroid cartilage, where it terminates by dividing into the internal and external carotid arteries.

2

Internal Carotid

continues upward in the carotid sheath through the submandibular and parotid spaces to enter the cranial cavity via the carotid canal. It gives off no branches in the neck.

3

External Carotid

ascends through the submandibular and parotid spaces to terminate at the neck of the mandible. During its course, it gives rise to nine branches, some of which already have been described. These branches may be divided into anterior, posterior, and ascending branches:

• A
  

  Anterior

  
  
  
  
  • 1
    

    External maxillary

    
    
  • 2
    

    Lingual

    
    
  • 3
    

    Superior thyroid

  
  
  
  
• B
  

  Posterior

  
  
  
  
  • 1
    

    Posterior auricular

    
    
  • 2
    

    Occipital

    
    
  • 3
    

    Sternocleidomastoid

  
  
  
  
• C
  

  Ascending

  
  
  
  
  • 1
    

    Superficial temporal

    
    
  • 2
    

    Internal maxillary

    
    
  • 3
    

    Ascending pharyngeal (not illustrated)

  
  

1

Internal Jugular Vein

in the upper part of the carotid triangle, this vein receives the common facial, lingual, and superior thyroid veins. In the lower portion of the triangle, the middle thyroid vein empties into it. The venous pattern in this area is extremely variable.

2

Vagus Nerve

gives off an important branch in the submandibular triangle: the superior laryngeal, the branches of which may be seen here. The internal branch may be identified piercing the thyrohyoid membrane at the lateral border of the thyrohyoid muscle. It carries sensory fibers from the larynx above the vocal cords. The external branch descends in association with the superior thyroid artery and innervates the cricothyroid and some fibers of the inferior constrictor.

3

Spinal Accessory Nerve

extends posteriorly deep to the sternocleidomastoid. Running with the nerve is the sternocleidomastoid artery, which may arise either from the external carotid or from the occipital artery.

4

Hypoglossal Nerve

winds forward under the occipital artery in the upper part of the triangle and proceeds into the submandibular triangle. It appears to give off a branch to the thyrohyoid, but this is actually a branch of the deep cervical plexus, which is discussed later ( Fig. 2 ).

5

Cervical Sympathetic Trunk

lies in the same position as in the submandibular triangle, posterior to the carotid sheath. This is not shown in the accompanying illustration.

1

Ansa Hypoglossi

a branch from C1 joins the hypoglossal nerve and after a short course divides into a branch supplying the thyrohyoid and geniohyoid and a descending branch, the descendens hypoglossi. Descending branches from C2 to C3 form the descendens cervicalis. These two branches join to form the ansa hypoglossi, which usually lies anterior to the carotid sheath. It is from these cervical branches that the strap muscles receive their innervation.

2

Phrenic Nerve

arises primarily from the anterior primary division of C4 but may receive slips from C3 or C5. This is discussed more fully later.

1

Anterior Scalene

arises from the anterior tubercles of C3 to C6 and inserts on the scalene tubercle (Lisfranc’s) on the upper surface of the first rib.

2

Middle Scalene

arises by slips from the transverse processes of C1 to C6 and is the largest of the scalenes. It also inserts on the first rib on a tubercle behind the groove for the subclavian artery.

3

Posterior Scalene

may be regarded as fibers of the middle scalene, which gain attachment to the lateral surface of the second rib. Like the other scalenes, these fibers are innervated by branches of the anterior rami of the cervical nerves.

4

Levator Scapulae

arises from the transverse processes of the first four cervical vertebrae and inserts on the vertebral border of the scapula. It is innervated by both the deep cervical plexus and the dorsal scapular branch of the brachial plexus.

In addition to the aforementioned muscles, the splenius capitis and the semispinalis capitis are present in the apex of the occipital triangle. Both belong to the spinal group of muscles and are innervated by the posterior primary divisions of the cervical nerves.

1

Anterior Primary Divisions

arise from C5 through T1 and are located behind the anterior scalene. Two main branches are given off from these parts: the dorsal scapular from C5, which innervates the rhomboids and the levator scapulae, and the long thoracic from C5, C6, and C7, which supplies the serratous anterior.

2

Trunks

form at the lateral border of the anterior scalene. The anterior primary divisions of C5 and C6 join to form the upper trunk, C7 continues as the middle trunk, and C8 and T1 unite to form the lower trunk. The upper trunk is the only one that gives rise to any branches; these are the suprascapular, which extends into the scapular region to supply the supraspinatus and infraspinatus, and the subclavius, which innervates the subclavius muscle.

3

Secondary Divisions

arise just behind the clavicle, each trunk dividing into an anterior and a posterior secondary division.

4

Cords

are located in the axilla. All posterior secondary divisions join to form a posterior cord. The anterior secondary divisions of upper and middle trunks form the anterolateral cord, and the anterior secondary division of the lower trunk continues as the anteromedial cord. The cords and their terminal divisions are discussed later.

1

Subclavian Vein

lies superficial in position in front of the anterior scalene but usually does not rise above the clavicle. It receives the external jugular in the posterior triangle, and on the left side, the thoracic duct may enter more lateral than usual, thereby passing anterior to the anterior scalene.

2

Subclavian Artery

lies behind the anterior scalene, the muscle dividing the artery into three parts: the first lying medial to the muscle, the second behind, and the third lateral to the muscle.

• A
  

  First portion–gives rise to three branches: the vertebral, internal mammary, and thyrocervical trunk. The inferior thyroid branch of the thyrocervical trunk passes behind the carotid sheath to the posteromedial surface of the gland (not to the inferior pole) and sends off anastomotic branches to the superior thyroid, as well as tracheal and esophageal branches. The remaining two branches from the trunk cross in front of the anterior scalene superficial to the deep layer of cervical fascia. The transverse cervical is superior in position and extends across the posterior triangle to the anterior border of the levator scapulae muscle, where it divides into an ascending and a descending (posterior scapular) branch. The transverse scapular also passes in front of the muscle and extends laterally behind the clavicle to the supraspinatus and infraspinatus fossae.

  
  
• B
  

  Second portion–gives rise to only one branch, the costocervical trunk, which, because of its position behind the anterior scalene, is rarely of concern to the surgeon. This trunk gives rise to the deep cervical and superior intercostal arteries (not illustrated).

  
  
• C
  

  Third portion–usually has no branches. However, one may find a transverse cervical (German) arising here, which, if present along with the transverse cervical of the first portion (British), becomes the posterior scapular or descending branch.

3

Brachial Plexus

anterior primary divisions of the plexus are located directly behind the anterior scalene and the trunks of the plexus at the lateral border of the muscle.

4

Phrenic Nerve

is of prime importance because it supplies the muscle fibers of the diaphragm. The diaphragm develops in the cervical region and migrates downward, thus explaining its cervical innervation. The nerve arises from the anterior primary division of C4. However, it often receives fibers from C3 and C5. It takes a very characteristic course over the anterior scalene, passing downward from lateral to medial and deep to the deep layer of fascia. In many cases, the accessory phrenic is present. The three most common sites are (1) a branch from C5 passing downward lateral to the phrenic and joining it either in the root of the neck or in the subclavian triangle and thence into the thorax, (2) a branch from C5 incorporated with the nerve to the subclavius and passing into the thorax anterior to the subclavian vein (see Fig. 1 ), or (3) a branch from C3 incorporated in the ansa hypoglossi and joining the phrenic in the thorax.

5

Spinal Accessory Nerve

is not directly related to the anterior scalene but is the uppermost structure of importance in the posterior triangle. It takes exit from under the sternocleidomastoid at the junction of its upper and middle third and descends parallel with the fibers of the levator scapulae. It then disappears beneath the trapezius, which it innervates. During its course, the nerve is joined by a communicating branch from the deep cervical plexus; running below and parallel to it are muscular branches from the deep cervical plexus to the trapezius muscle (see Fig. 1, Plate 3 ). The latter nerves may be mistaken for the spinal accessory. The previously mentioned nerves lie in a plane between the superficial and deep layers of the cervical fascia. They are the only motor nerves that lie superficial to the deep layer of deep cervical fascia.

1

Apex

is formed by the clavicle, the upper border of the first rib, and the superior border of the scapula.

2

Base

is made up of the skin of the axilla, the superficial fascia, and the axillary fascia, a continuation of the pectoral fascia.

3

Anterior Wall

consists of pectoralis major and minor and is innervated by the antero medial and antero lateral cords via medial and lateral anterior thoracic nerves.

• A
  

  Pectoralis major–arises by a clavicular, sternal, and abdominal head and inserts into the lateral lip of the bicipital groove.

  
  
• B
  

  Pectoralis minor–takes origin by slips from the second to fifth ribs and inserts on the coracoid process of the scapula.

4

Posterior Wall

is made up of three muscles, which, from superior to inferior, are the subscapular, teres major, and latissimus dorsi, all of which are innervated by the posterior cord via the subscapular nerves.

• A
  

  Subscapular–arises in the subscapular fossa and inserts into the lesser tubercle of the humerus.

  
  
• B
  

  Teres major–takes origin from the inferior angle of the scapula and extends to the medial lip of the bicipital groove.

  
  
• C
  

  Latissimus dorsi–has an extensive origin from the dorsum of the body and terminates in the bicipital groove.

5

Lateral Wall

consists of two muscles, the coracobrachialis and the short head of the biceps, both arising from the coracoid process and innervated by the antero lateral cord via the musculocutaneous nerve.

• A
  

  Coracobrachialis–extends from the coracoid process to the middle third of the shaft of the humerus.

  
  
• B
  

  Short head of the biceps–arises in common with the coracobrachialis and inserts, after joining the long head, into the radius and the antebrachial fascia.

6

Medial Wall

is formed by the upper digitations of the serratus anterius. It is innervated by the long thoracic nerve from anterior primary divisions of the brachial plexus.

S erratus anterius –arises from digitations from the upper nine ribs and inserts into the vertebral border of the scapula.

1

Pectoral Fascia

encloses the pectoralis major and extends from the lower border of the muscle to become axillary fascia extending posteriorly as the fascia of the latissimus dorsi. Laterally, it is continuous with the investing fascia of the arm.

2

Clavipectoral Fascia

extends from the clavicle above to the axillary fascia below. It surrounds the subclavius and pectoralis minor muscles. Between the subclavius and pectoralis minor, this fascia is thickened to form the costocoracoid membrane, which is pierced by the cephalic vein, thoracoacromial vessels, and the anterior thoracic nerves. After splitting around the pectoralis minor, the fascia fuses and joins the axillary fascia to form the suspensory ligament of the axilla.

3

Axillary Sheath

is a prolongation of the deep layer of the deep cervical fascia enclosing the axillary vessels and branches of the brachial plexus. It extends for a variable distance into the axilla.

Axillary Vein ( Fig. 3 )

With the upper extremity in the abducted position, the main structure brought into view is the axillary vein and its tributaries. More superficial, however, are the lateral cutaneous branches of the upper intercostal nerves; that from T2, passing to the medial side of the brachium, is termed the intercostobrachial nerve.

At the lower border of the teres major, the basilic vein joins the brachial veins to form the axillary vein, which extends upward to the lower border of the first rib. Here the vein is termed the subclavian. Its tributaries follow the branches of the axillary artery, except for the following:

1

Cephalic Vein

arises on the dorsum of the hand, passes upward in the superficial fascia of the upper extremity, and pierces the costocoracoid membrane at the deltopectoral triangle. It empties into the axillary vein above the pectoralis minor. This vessel serves as a collateral channel for venous return from the upper extremity after occlusion of the axillary vein. It also serves as a guide to the first portion of the axillary artery.

2

Thoracoepigastric Vein

connects the superficial epigastric below with the lateral thoracic branch of the axillary above, thus serving as an important collateral pathway after obliteration of the inferior vena cava.

1

First Portion

is located between the first rib and the upper border of the pectoralis minor and gives off one branch.

S upreme thoracic –passes behind the axillary vein and across the apex of the axilla to supply the structures in the first intercostal space.

2

Second Portion

is found behind the pectoralis minor and usually gives rise to two branches:

• A
  

  Thoracoacromial–pierces the costocoracoid membrane and divides into branches directed toward the clavicle, acromion process, and the deltoid and pectoral muscles.

  
  
• B
  

  Lateral thoracic–descends along the medial wall of the axilla to about the fifth intercostal space. It sends branches to the muscles of the anterior and medial walls of the axilla and mammary gland.

3

Third Portion

extends from the lower border of the pectoralis minor to the lower border of the teres major. Three branches arise from this third portion (see Figs. 1 and 2 ):

• A
  

  Subscapular–extends toward the posterior wall of the axilla and terminates as the circumflex scapular and thoracodorsal. The former pierces the posterior axillary wall through a muscular interval, bounded by the subscapular, teres major, and long head of the triceps (triangular space), and reaches the infraspinatus fossa. The thoracodorsal continues through the axilla to the inferior scapular angle.

  
  
• B
  

  A nterior circumflex humeral –is a small branch that passes deep to the coracobrachial and biceps tendons and winds around the surgical neck of the humerus.

  
  
• C
  

  P osterior circumflex humeral –arises opposite the anterior circumflex branch and winds around the surgical neck of the humerus to anastomose with the anterior branch. It pierces the posterior wall of the axilla through a space bounded by the shaft of the humerus, teres minor, teres major, and long head of the triceps (quadrilateral space). It is accompanied in this space by the axillary nerve. The artery gives off an important anastomotic branch to the profunda brachii.

1

Anterolateral Cord

• A
  

  L ateral – anterior thoracic –pierces the costocoracoid membrane and supplies the pectoral muscles.

  
  
• B
  

  M usculocutaneous –is the most lateral of the terminal branches and innervates the muscles of the lateral wall of the axilla, the coracobrachialis, and the biceps. It pierces the coracobrachial as it descends to the arm.

  
  
• C
  

  L ateral head of the median –forms the lateral component of the median nerve.

2

Anteromedial Cord

• A
  

  M edial – anterior thoracic –joins the lateral anterior thoracic to innervate the pectoral muscles.

  
  
• B
  

  M edian head of median –passes obliquely over the third part of the axillary artery to join the lateral head from the anterolateral cord to form the median nerve. The latter lies along the lateral side of the artery.

  
  
• C
  

  U lnar –is the largest of the medial cord branches and arises at the lower border of the pectoralis minor. It descends into the arm along the medial side of the axillary artery.

  
  
• D
  

  M edial antebrachial cutaneous –arises in close relation with the ulnar nerve.

  
  
• E
  

  M edial brachial cutaneous –lies medial to axillary vein in the lower axilla; pierces the deep fascia and is distributed to the skin of the medial surface of the arm.

3

Posterior Cord (see Fig. 2 )

• A
  

  S ubscapular nerves –usually three in number and termed the upper, middle, and lower. They supply the muscles of the posterior wall of the axilla; the upper innervates the subscapular; the middle (thoracodorsal), the latissimus dorsi; and the lower, the teres major.

  
  
• B
  

  A xillary –extends dorsally and leaves the axilla via the quadrilateral space accompanied by the posterior humeral artery and innervates the deltoid and teres minor muscles.

  
  
• C
  

  R adial nerve –is a direct continuation of the posterior cord lying behind the axillary artery. It is the largest terminal branch of the brachial plexus.

1

Posterior (Subscapular)

six or seven in number; along the subscapular vessels and thoracodorsal nerve.

2

Lateral (Brachial)

four or five in number; along lower part of axillary vein.

3

Anterior (Anterior Pectoralis)

four or five in number; along edge of the pectoralis major.

4

Medial (Posterior Pectoral)

three or four; along the lateral thoracic artery and vein.

5

Central

three to five; lies at the base of the axilla in the fatty tissue.

6

Apical (Infraclavicular)

four or five; at apex of triangle, closely related to axillary vein.

Intrinsic Muscles

lie in the anterior or flexor compartment and are innervated by the musculocutaneous nerve.

• 1
  

  C oracobrachialis –arises from the coracoid process of the scapula and inserts at the middle of the medial surface of the shaft of the humerus. It is pierced by the musculocutaneous nerve. This muscle acts as a flexor and adductor of the arm at the shoulder.

  
  
• 2
  

  B iceps brachii –the short head arises from the coracoid process; the long head takes origin from the supraglenoid tuberosity of the scapula. The biceps tendon inserts mainly into the radial tuberosity; however, some of its fibers expand medially and downward to insert in the antebrachial fascia (lacertus fibrosus) (see Fig. 2 ). Aside from its function as a flexor of the forearm, it acts as a very strong supinator.

  
  
• 3
  

  B rachialis –takes origin from the lower three fifths of the shaft of the humerus under cover of the biceps and inserts on the coronoid process of the ulna. In addition to its innervation by the musculocutaneous, the lower lateral fibers usually receive a twig from the radial. It serves to flex the arm at the elbow.

1

Musculocutaneous Nerve

leaves the bundle in the upper arm, pierces the coracobrachialis, then descends between the brachialis and biceps, and continues superficially as the lateral antebrachial cutaneous. It supplies the three intrinsic muscles of the anterior compartment: the coracobrachialis, biceps, and brachialis.

2

Median Nerve

is formed by the medial and lateral heads as described in the axilla. In the upper arm, the nerve lies lateral to the brachial artery, but in its descent through the arm, it crosses anterior to the artery and comes to lie on the medial side in the lower arm and cubital region. It gives off no branches in the arm.

3

Ulnar Nerve

lies along the medial border of the brachial artery in the upper arm. At the insertion of the coracobrachialis, it pierces the medial intermuscular septum and enters the posterior compartment. It gives off no branches in the arm.

4

Brachial Artery

supplies the entire brachium. It begins at the lower border of the teres major as a continuation of the axillary and terminates at the elbow by dividing into a radial and ulnar branch. In addition to its muscular and nutrient branches, its main trunks are as follows:

• A
  

  D eep brachial ( profunda )–is the largest branch and leaves the bundle in the upper arm to enter the posterior compartment accompanied by the radial nerve.

  
  
• B
  

  S uperior ulnar collateral –arises from the brachial about midarm, pierces the medial intermuscular septum, and accompanies the ulnar nerve into the posterior compartment.

  
  
• C
  

  I nferior ulnar collateral –takes origin just above the elbow from the medial side of the brachial descending anterior to the medial epicondyle.

The brachial artery is accompanied by two brachial veins: the venae comitantes. At the lower margin of the teres major, these two veins join along with the basilic vein to form the axillary vein.